What's your best response to "I don't know why this isn't working"?

Mine was a few years ago, when a colleague sitting next to me started asking herself "Why isn't this working? I don't understand it! I've tried anything I can think of..."
At this point I've turned to her and asked "Well, Did you sacrifice a goat?"

BTW, she found and fixed the bug the second she started to explain the problem to me.

Comments

[Stephen Chiang]

'Try restarting the machine/server'

Or

It works on my machine

[Fulton Browne]

Have you googled it?

[Pan Chasinga]

Did you pray to Jon Skeet?

[Jakob Attkinson]

FYI: that's called "rubber duck debugging".